1. Technical Field
The present invention relates to an optical device that requires an optical spatial resolution, and in particular, relates to an optical device that focuses a light beam onto an observation sample and relatively changes the light beam irradiation position with respect to the observation sample to acquire a response signal.
2. Background Art
A scanning optical microscope scans an observation sample (a sample to be observed) with a light beam by narrowing the light beam into a minute spot down to the diffraction limit. It is known that when a light beam from an observation sample is detected with a large area detector, the same resolution as that of a conventional microscope is attained. The conventional optical microscope as referred to herein irradiates a wide range of an area of an object with a light beam, and forms an image of the irradiated object through an objective lens. It is known that when a response beam of the beam, which has been focused onto the observation sample, is detected through a pinhole, the resolution will improve (Non-Patent Document 1). This is commercially available as a confocal scanning optical microscope.
There are known two scanning methods for the confocal scanning optical microscope. One is a method of directly moving an observation sample with respect to a focused spot. This method is advantageous in that the design of the optics is easy, optical aberrations generated in the optical spot are small, the scanning range is wide, and the like. However, this method is disadvantageous in that the scanning time is difficult to be reduced, a soft observation sample in a liquid could shake due to the scanning, and the like. The other scanning method is a method of fixing an observation sample and moving a scanning optical spot. This method can increase the scanning speed and can also handle a soft observation sample in a liquid. However, this method is disadvantageous in that the scanning optics are complex.
FIG. 11 shows optics of a reflection-type confocal scanning optical microscope. The scanning method used herein is a method of moving a scanning light beam. A laser beam emitted from a laser source 101 is collimated by lenses 261 and 208, and is reflected by a half mirror 262, and then enters a two-dimensional scanning mechanism 263 as an incident beam 302. The two-dimensional scanning mechanism includes two galvanometer mirrors, for example. The angle of the light beam output from the two-dimensional scanning mechanism 263 with the optical axis changes due to the scanning, and is obliquely output like an output light beam 300, for example. The light beam output from the two-dimensional scanning mechanism 263 is, after entering an objective lens 201, focused as a minute spot onto an observation sample 202. A laser beam 301 with such a minute light spot is reflected by the observation sample 202, and then returns back to the objective lens 201. The angle of the laser beam, which returns from the objective lens 201 to the two-dimensional scanning mechanism 263, with the optical axis is the same as that when the laser beam has entered the two-dimensional scanning mechanism 263. Therefore, the returning laser beam propagates along the same optical path as the incident light beam within the two-dimensional scanning mechanism, and becomes, when output from the two-dimensional scanning mechanism, a light beam that propagates along the same optical path as the fixed incident light beam 302. A reflected laser beam from the observation sample passes through the half mirror 262, and is focused onto a pinhole 265 by a condenser lens 264. Then, the transmitted beam is detected with a photodetector 104. The focused position of the laser beam on the pinhole 265 is not displaced regardless of the beam scanning. Thus, the detected intensity of the laser beam from the observation sample is not influenced by the scanning. Reference numeral 109 denotes an electronic device that captures a detection signal and controls the scanning position. The detection signal is displayed as an image on a display device 110.
FIG. 12 shows optics of a transmission-type confocal scanning optical microscope. In this case, a method of moving an observation sample to be scanned is adopted. A laser beam emitted from a laser source 101 is collimated by lenses 261 and 208 and is reflected by a half mirror 262. Then, the laser beam enters an objective lens 201 and is focused onto an observation sample 202. A laser beam that has passed through the observation sample 202 is focused onto a pinhole 265 by an objective lens 207 whose properties are close to the numerical aperture of the objective lens 201, and a condenser lens 205. A laser beam that has passed through the pinhole 265 is detected with a photodetector 104, and is captured by an electronic device 109. Scanning is performed by moving the observation sample 202. That is, the electronic device 109 moves and controls the position of a stage 200 that is integrated with the observation sample 202, using an actuator 102. When cells of a living organism and the like are observed as described above, a technology of slowly moving the stage 200, or fixing the cells on a holder fixed on the stage 200 should be used.    Non-Patent Document 1: T. Wilson, and C. Sheppard: Theory and Practice of Scanning Optical Microscopy: Academic Press, London (1984)